Sawing machines are classified according to basic machine design, i.e., band saw, gang saw, chain saw, circular saw and they are further classified according to the specific operation for which they are used. A head saw is the primary log break-down saw in a saw mill and a resaw is one used for ripping the so produced cant into boards. The primary distinction between a head saw and a resaw, where each is of the circular saw type, is the diameter of the circular saw blade. Typically resaws have a diameter under 30 inches and the head saw circular blades are in the range of 34 to 60 inches. The latter are referred to as large diameter circular saw blades while the former are referred to as small diameter circular saw blades.
Large diameter saw blades are conventionally thicker than small diameter saw blades and conventionally head saws have removably insertable teeth. In order to removably insert the teeth the gullet must be machined to receive a shank and a removable bit. The shank and bit and machining of the gullet contributes to a costly saw blade and high maintenance costs.
As discussed in the foregoing, a first major distinction between head saws and resaws is the diameter of the blade and the second distinction is the difference in the blade construction. It is known to use thin-kerf blades for small diameter saw blades but thin-kerf blades have not been used for large diameter blades in head saws to applicant's knowledge. The removable tooth and machined gullet is also another distinction present in the head saws but not in resaws.
A further distinction between head saws and resaws is that the latter are normally ganged on a common shaft and float axially along the shaft, guides being used to maintain the position of the floating saws to ensure accuracy and consistency in cutting the multiple boards from a cant. This is possible because the blades are always in a plane parallel to the path of travel of the cant being cut. There is no "lead angle" as required in head saws. Further discussion of this will occur later. Examples of ganged blade resaws are found in the teachings of U.S. Pat. No. 3,817,143 issued Jun. 18, 1974 to A. U. Jones and U.S. Pat. No. 3,703,915 issued Nov. 28, 1972 to H. C. Pearson. Both of these references teach the use of thin-kerf blades on small diameter blade resaws where the saw blade is shiftable along the arbour and kept in line by means of guides. The guide in U.S. Pat. No. 3,817,143 is located at the in-feed side of the saw and at the out-feed side of the cut, i.e., below the cut in the cant during operation of the saw. In U.S. Pat. No. 3,703,915 the guide is provided with two spaced apart contact pads on each of opposite sides of the blade, the guide being located at the in-feed side of the cant and at the in-feed side relative to the cut in the cant during operation of the saw. Another example of a thin-kerf guided saw that floats on a saw arbour is found in the teachings of U.S. Pat. No. 3,550,654 issued Dec. 29, 1970 to E. W. Thrasher. Further examples of ganged and guided saw blades are found in the teachings of Canadian Patents 1,272,274 issued Jul. 31, 1990 and 1,224,702 issued Jul. 28, 1987. Head saws differ from resaws by having the saw blade fixed to the arbour instead of floating.
Saw blade guides are known for guiding blades that are fixed to a mandrel for rotation therewith and by way of example reference may be had to the following U.S. Pat. Nos. 848,548 issued Mar. 26, 1907 to A. Harrold; 561,411 issued Jun. 2, 1896 to A. Marks; 140,157 issued Jun. 24, 1873 to F. Palmer; 292,331 issued Jan. 22, 1884 to W. Liddell; 394,110 issued Dec. 4, 1888 to D. Fraser; 173,907 issued Feb. 22, 1876 to J. Collins; 378,513 issued Feb. 28, 1888 to J. Marshall; 385,131 issued Jun. 26, 1888 to D. Murray. In these patents the majority of the saw guides are adjustable and have removable or replaceable pads that engage the side face of the blade. Further examples of adjustable saw guides variously constructed will be found in the teachings of U.S. Pat. Nos. 222,396 issued Dec. 9, 1879; 128,776 issued Jul. 9, 1872; 341,055 issued May 4, 1886; 186,541 issued Jan. 23, 1877; 535,325 issued Mar. 5, 1895 and 270,387 issued Jan. 9, 1883. These guides are all single pad contact types.
There exists today a number of saw mills in small to medium operations where replacement of existing equipment is uneconomic but with some changes to existing equipment the now considerable wastage and slow production could be improved.